In printing systems, printheads and substrates on which they print move relative to one another. To synchronize the emission of the material from the printheads to particular locations on the substrates, clocks, devices that measure substrate movement distances, and position detectors are used. The signals generated by these components are received by a controller and analyzed to determine the speed of a moving substrate or printhead and to determine a future time at which an ejector in the printhead is opposite a particular position where material should be ejected. A signal that activates the ejector is sent to the ejector immediately before that position is reached so the ejector is activated to eject a drop of material at the predetermined position.
In some known inkjet printers, the signals that activate ejectors in printheads are called DotClock signals. These DotClock signals are typically based on positional input from an encoder that is associated with a roller that moves a substrate through the printer prior to the substrate being printed. These rotary encoders are optical or electromagnetic sensors that convert the angular position of the roller from an index position into an electrical signal. With information regarding the radius or diameter of the roller along with the current angular position, the controller can determine when a portion of the substrate currently at the roller is positioned elsewhere in the printer. This positional data, rather than strictly time-based data, is used so variation in the substrate transport speed can be taken into account, which results in significant accuracy of substrate location positions. In other known systems, a linear encoder is used to convert the linear position of a tag on a component carrying a substrate as the component moves through the system into an electrical signal that is used as positional data for substrate movement.
Printing system technology has been adapted to form electronic circuits on flexible substrates. In these printing systems, a printhead array ejects conductive ink onto the flexible substrates to form ink images of electronic traces on the substrates. The printed flexible substrates bearing the liquid ink images of the electronic traces are then moved past a sintering head that exposes the liquid ink image to an intense light that hardens the liquid ink and bonds the traces to the substrate. The substrates continue to move past the sintering head to another machine that populates the flexible substrates with electronic components and applies solder to install the components in the electronic traces. The completed flexible substrates can then be installed in devices. Operating the lamps in sintering heads differs from known printhead activation technology because the DotClock signals for inkjet printheads react to the rising edge of the signal and the duration of the pulse in the signal is not important. The lamps in the sintering heads, however, require the activation signal to remain at the activating amplitude to keep the lamp shining while the printed circuits are opposite the lamps. The DotClock signal in known inkjet printers provide a rising edge that precisely indicates that a position on a substrate has traveled a specific distance and reached a particular location at a specific point in time. This signal, however, does not have to maintain the amplitude present at the rising edge for the ejector since it only ejects one drop and does not eject another drop until another DotClock signal is received. Rather than redesigning the DotClock signal generator that drives a sintering head so it produces activation signals for the lamps in sintering heads that correspond to different periods of illumination for different lengths of circuits formed on flexible substrates, a less drastic modification of the DotClock signal generator operation would be beneficial.